The invention relates to an earth drilling device for drilling a borehole into the soil and/or for pulling a pipe into an underground channel.
Such earth drilling devices are used for a trenchless installation of utility lines, such as fresh water or wastewater lines, gas lines, telecommunication lines or electrical power cables, drainage pipes as well as geothermal probes into the soil or for a trenchless replacement of an already existing line.
Various different earth drilling devices are known in the art, wherein the earth drilling device to be used are typically selected depending on the type of the line to be installed, the length of the line to be installed or to be replaced, the accessibility of the start and target region of the line segment to be installed or replaced, and particularly also depending on the condition of the soil in which the line is to be installed or replaced.
A widely used type of earth drilling devices includes a drive unit which can be arranged in the start region (in an excavation pit, a shaft as well as at a location on the surface) of a borehole to be drilled and which drives a drill rod with a drill head disposed at the front end for driving the drill head through the soil along the desired drilling path. With such earth drilling devices, a pilot hole extending from the start region to a target region (likewise an excavation pit, a shaft or a location on the surface) is typically introduced into the soil in a first drilling operation. The drill head is then replaced in the target region by an expansion head to which the pipe to be pulled into the borehole can be attached. When the drilling rod with the attached expansion head and the new pipe are retracted with the drive unit, the previously produced pilot bore is expanded and the new pipe is simultaneously pulled in.
Another type of widely used earth drilling devices relates to the so-called earth rockets. These are self-propelled drilling rams which include an internal impact drive used to intermittently advance the earth rocket through the soil. The impact drive is continuously supplied with the required energy via compressed air which is supplied to the earth rocket through a trailing supply hose.
Until now, earth rockets have primarily been used to introduce pilot bores into the soil. In a subsequent operation, an expansion head to which the new pipe to be pulled is attached is then pulled through the pilot bore with a pulling device, whereby the pilot bore is expanded and the new pipe is pulled in. The new pipe has typically not been pulled directly with the earth rockets because of the problematic attachment of the new pipe to the earth rocket due to the intermittent impact operation of the earth rocket, which regularly caused damage to the new pipe. Because improvements in the attachment of a new pipe to an earth rocket have since been made, a direct pipe replacement, wherein the new pipe is directly attached to the earth rocket, is now more frequently used.
Impact drilling processes where the new pipe is advanced in the soil by applying pressure forces are used regularly only with pipes having a very large diameter. In the aforedescribed direct pipe replacement with an earth rocket—as well is in almost all other processes for trenchless installation of a pipe—the new pipe is pulled through the underground channel, i.e., by applying pulling forces which are applied to the new pipe either at the front via an adapter or via a pulling element and from the back end via a rear adapter. In the second case, although the new pipe is pulled in by a pulling process, the new pipe is actually rather pushed. When the pulling forces are applied to the front end of the new pipe, the new pipe is frequently additionally tensioned against the earth drilling device by a pulling element (e.g., pulling cable, chain, pulling rods) extending through the new pipe and a corresponding rear adapter, so as to prevent the pipe segments in a pipe string consisting of individual pipe segments from becoming detached from each other. In a long pipe which is typically made of plastic, tensioning may prevent overstretching of the plastic. A corresponding system for tensioning a new pipe in an earth drilling device is disclosed, for example, in DE 196 08 056 C1. Like essentially all components of an earth drilling device, the pulling element as well as the tensioning adapter are also made of a metal and in particular steel, because steel is inexpensive and withstands high mechanical stress. Metals, such as steel, also have a very high electrical conductivity.
In particular in a direct pipe replacement with an earth rocket, where the drilling the borehole and pulling in the new pipe occurs simultaneously, problems may be encountered when the earth rocket hits a current-conducting underground cable, partially destroying the underground cable. This has the risk that the current is conducted via the earth rocket and the frequently metal-reinforced and hence also electrically conducting supply hose and via the tensioning element provided for tensioning the new pipe to the start region, which can potentially endanger an operator coming into contact with these current-carrying cables.
Based on this conventional technology, it was the object of the invention to reduce the risk of endangering an operator when an earth drilling device hits a current-carrying underground cable.